Wireless networks might be mainstream across enterprise networks, but that doesn't mean they're no-brainers. Over the next few weeks we attempt to answer some of the thornier questions you might still be dealing with.

A surprising number of wireless LAN vendors have recently announced enterprise access points based on the draft IEEE 802.11n standard, promising throughput of 100 Mbit/s to 200 Mbit/s per frequency band, or from three to six times that of today's 11g and 11a nets.

Whether network managers opt for the draft 11n products, certified interoperable by the Wi-Fi Alliance, or wait for the final IEEE ratification in late 2008 or early 2009, they could face any of these four issues: overloading part of the wired infrastructure; overloading existing, older wireless LAN switches; forcing an upgrade to higher-powered Power-over-Ethernet; and repositioning and rewiring some number of existing wireless access points.

More Gigabit ports

Most of the new access points will come with one or even two Gigabit Ethernet ports. "We're mostly '100 meg' to our buildings," says Michael Dickson, network analyst at University of Massachusetts at Amherst. "[For 11n,], we'll need gigabit switches in the closet with 10-gigabit uplinks. That's a definite cost, almost a necessary cost for 11n."

"11n adds an incentive to go to 'gigE' [in the wired infrastructure]," says Craig Mathias, principal with Farpoint Group.

One related issue with upgrading a cable plant, given the capacity of 11n, is whether to upgrade the Ethernet wall jacks, a decision about whether the wireless infrastructure becomes the principal means of network access.

If existing wireless LAN controllers also lack the net capacity, and the needed processing power and memory to handle the increased traffic, they'll have to be replaced, especially if the vendor has a purely centralised architecture with every packet running from each access point to the controller. Vendors have been upgrading their controllers over the past year with 11n in mind, sometimes also offloading the packet switching functions to the access points, creating a distributed data plane.

"With this kind of distributed data plane, there's no bottleneck at the controller," says Mathias. "If you have Meru or Extricom, you have centralised data and control planes. But if you design the box to handle whatever is thrown at it, it's not a problem."

Benchmarking wireless performance to verify such things as workloads and traffic conditions is likely to become much more important for 11n nets. To do this, enterprises or systems integrators will use complex performance-testing tools, such as those from VeriWave and Azimuth Systems, which previously had been used mainly by radio chip makers and equipment manufacturers. "This will be a big thing down the road," Mathias predicts.

Don't forget the power problem

The Power over Ethernet (PoE) issue may catch some users by surprise. "The PoE infrastructure may have its upper limits tested by 11n deployments [that are] used to their maximum capabilities," says Chris Silva, analyst at Forrester Research.

PoE lets you run just one cable between switch and access point, instead of two, potentially a big cost saving. But the 11n access points draw more electricity than the 15.4 watts maximum provided by power injectors based on the IEEE 802.3af standard. That will at least double with a new standard, 802.3at, now being finalised. At least one vendor, Trapeze, has created new code that can let its just-announced 11n access point make use of existing PoE injectors, but there are tradeoffs in terms of performance.

"The promise of 11n is more than simply going faster," says Phil Belanger, managing director for Novarum. "The increased range of 11n will make it more practical to deploy large systems using the 5-GHz band, which has many more channels than the 2.4-GHz and has not been used very much to date. That, in turn, will enable much higher capacity wireless LANs. For many enterprises, a wireless network that delivers hundreds of megabits of capacity everywhere will be good enough to be the only network."